Rapid growth of Moso bamboo (Phyllostachys edulis): Cellular roadmaps, transcriptome dynamics, and environmental factors.

Moso bamboo (Phyllostachys edulis) shows remarkably rapid growth (114.5 cm/day), but the underlying biological mechanisms remain unclear. After examining more than 12,750 internodes from more than 510 culms from 17 Moso populations, we identified internode 18 as a representative internode for rapid growth. This internode includes a 2-cm cell division zone (DZ), a cell elongation zone up to 12 cm, and a secondary cell wall (SCW) thickening zone. These zones elongated 11.8 cm, produced approximately 570,000,000 cells, and deposited ∼28 mg g-1 dry weight (DW) lignin and ∼44 mg g-1 DW cellulose daily, far exceeding vegetative growth observed in other plants. We used anatomical, mathematical, physiological, and genomic data to characterize development and transcriptional networks during rapid growth in internode 18. Our results suggest that (1) gibberellin may directly trigger the rapid growth of Moso shoots, (2) decreased cytokinin and increased auxin accumulation may trigger cell DZ elongation, and (3) abscisic acid and mechanical pressure may stimulate rapid SCW thickening via MYB83L. We conclude that internode length involves a possible tradeoff mediated by mechanical pressure caused by rapid growth, possibly influenced by environmental temperature and regulated by genes related to cell division and elongation. Our results provide insight into the rapid growth of Moso bamboo.

Cellular and molecular characterizations of the irregular internode division zone formation of a slow-growing bamboo variant.

The key molecular mechanisms underlying the sectionalized growth within bamboo or other grass internodes remain largely unknown. Here, we genetically and morphologically compared the culm and rhizome internode division zones (DZs) of a slow-growing bamboo variant (sgv) having dwarf internodes, with those of the corresponding wild type (WT). Histological analysis discovers that the sgv has an irregular internode DZ. However, the shoot apical meristems in height, width, outside shape, cell number and cell width of the sgv and the WT were all similar. The DZ irregularities first appeared post apical meristem development, in 1-mm sgv rhizome internodes. Thus, the sgv is a DZ irregularity bamboo variant, which has been first reported in bamboo according to our investigation. Transcriptome sequencing analysis finds that a number of cell wall biogenesis and cell division-related genes are dramatically downregulated in the sgv DZ. Interestingly, both transcriptomic and brassinosteroid (BR) contents detection, as well as quantitative real-time PCR analyses show that these irregularities have resulted from the BR signaling pathway defects. Brassinosteroid defect might also cause the erect leaves and branches as well as the irregular epidermis of the sgv. These results suggest that BR signaling pathway plays critical roles in bamboo internode DZ and leaf development from a mutant perspective and also explain the upstream mechanisms causing the dwarf internode of the sgv bamboo.